Microbiome seen as key factor in resilience/immunity equation

The microbiome plays a key role in determining how different individuals respond to psychological and physical stress, researchers have concluded.

In a review paper titled “Resilience and Immunity,”​​​ researchers from the MD Anderson Cancer Center in Houston, Mt Sinai Hospital in New York and University College Cork in Ireland explored the concept of resiliency. The paper was published in the journal Brain, Behavior and Immunity.​

The researchers defined resilience as: “[T]he process that allows individuals to adapt to adverse conditions and recover from them. This process is favored by individual qualities that have been amply studied in the field of stress such as personal control, positive affect, optimism, and social support.”​

Studies on pure psychology took the lead

They noted that psychologically resilient individuals tend to have more robust immune systems. It is a relationship that has been established by research stretching back more than 25 years. But much of that research focus on psychological factors first.

“Often neglected in the discussion of resilience and immunity is that the relationship between stress and immunity is not unidirectional as immune mediators can influence factors that contribute to resilience and stress outcomes. Both human and animal studies show that immune mediators influence the way the brain processes information and responds to it both physiologically and behaviorally,”​ the researchers wrote.

The authors noted that the literature supports the notion that resilient individuals have a different immunophenotype from that of stress-susceptible individuals and modifying their inflammatory phenotype renders them susceptible to stress and vice versa for stress-sensitive individuals.

Resilient individuals tend to have greater feelings of personal control, tend to be more optimistic and exhibit what psychologists refer to as ‘positive affect.’ They also tend to have better systems of social support, though this begs one of the many chicken-and-egg questions in this field of research. Do they have more social support because positive individuals form friendships more easily? Or does having more support boost optimism?

Psychological factors studied in isolation

A big complicating factor that the researchers took note of is that much of the research on resilience in humans has tended to take a compartmentalized approach. Each psychological factor, such as optimistic vs pessimistic individuals, or those with good supports systems vs those without, has been studied exhaustively in isolation.

Different studies have used different outcomes, making it difficult to correlate the results. Also, the information on stressors is lacking as well, they noted.

On the animal side, however, the picture has become much clearer. Just a couple of measures will suffice to determine if a mouse is depressed or not. And the stressors used, whether it be learned helplessness, swimming exhaustion, separation of mothers and young or what have you are well characterized. And, of course, many of these studies could not be conducted ethically with humans.

Development of psychobiotics

The researchers said that while there is broad agreement that gut dysbiosis can negatively affect mental states and therefore resilience, finding specific strains that operate in the opposite direction has proven to be a challenge. In their review of the literature, only a few specific Bifidobacterium and Lactobacillus strains have shown targeted cognitive effects, such as reductions in anxiety and perceived stress. Nevertheless, it is a field of great possibility, they said.

“There is evidence that decreased diversity of the microbiota negatively impacts resilience and increases the risk of depression/anxiety. Undoubtedly, poor diet and antibiotic exposure can lead to this state of dysbiosis with resultant vulnerability. Studies in healthy volunteers indicate that certain psychobiotics can improve resilience and may help prevent depression, while a modified Mediterranean diet may exert antidepressant effects probably also by acting through the microbiota. The impact of diet has traditionally been ignored by both psychiatrists and clinical psychologists but nutritional psychiatry is now emerging as an important field,”​ they wrote.